Eco-Friendly Process for the Preparation of 2-Chlorobenzylidene-Malononitrile (Cs)

ABSTRACT

An improved process for the preparation of 2-chlorobenzylidenemalononitrile (CS) comprising of the steps of: preparing malononitrile suspension by adding 5-20% (wt %) preferably 12-14% malononitrile to water while constantly stirring and then adding 0.05-0.5% (v/v) preferably 0.1-0% of a catalyst like piperidine, pyridine, 2-picoline, 3-picoline, 4-picoline or morpholine preferably piperidine piperidine with constant stirring at 20-30° C.; condensing the malononitrile suspension prepared in step (a) with 2-chlorobenzaldehyde by adding 10-15% (w/v) preferably 25-30%, of 2-chlorobenzaldehyde cover a period at 30-45 minutes so that the temperature of the reaction mixture remains below 50° C., constantly stirring for 20-40 minutes, then filtering the CS and drying it at 20-30° C. under water vacuum for 3-5 hrs.

FIELD OF INVENTION

This invention relates to an improved and eco-friendly process for thepreparation of 2-Chlorobenzylidenemalononitrile [CS,(2-chlorophenyl)methylene propanedinitrile] using water as a solvent.

PRIOR ART

2-Chlorobenzylidenemalononitrile (CS) was first reported by Corson andStoughton and was introduced as riot control agent in 1958. It is awhite crystalline solid, ten times more potent thanω-chloroacetophenone, a well known riot control agent. To produceimmediate effects on the eyes and respiratory tract, 4 mg/m³ CS issufficient. Exposure to CS results in immediate burning sensation ineyes, accompanied by copious flow of tears and involuntary closing ofeyes, irritation of respiratory tract results in sneezing, tightness inchest with difficulty in breathing and coughing. In high concentrations,CS causes nausea and vomiting.

One of the process known in the art, for the synthesis of CS, involvesKnoevenagel condensation of 2-chlorobenzaldehyde and malononitrile,either using organic solvents and pyridine or in absence of organicsolvents by grinding. The method reported by Corson and Stoughtoninvolves Knoevenagel condensation of 2-chiorobenzaldehyde withmalononitrile in the presence of pyridine using cyclohexane as solventfor the reaction. Another method (U.S. Pat. No. 3,963,770) uses methanolas solvent for the synthesis of CS.

The main disadvantage of these methods is that large quantity ofcyclohexane or methanol is required.

Another disadvantage of these methods is that the organic solvents,cyclohexane and methanol are toxic and inflammable.

Yet another disadvantage of these methods is that isolation of CS isdifficult at room temperature due to its solubility in both thesolvents.

Still another disadvantage of these methods is that due to the toxic andinflammable nature of the effluent, the disposal of effluent isdifficult and hence these processes are not environmental andeco-friendly.

Yet another disadvantage of these methods is that the cyclohexane is notrecycled in the former process, therefore the process is not, costeffective.

Another known process in the art for synthesis of CS involves solventfree Knoevenagel condensation of 2-chlorobenzaldehyde and malononitrileby grinding.

The major drawback of this method is that the reaction is applicable tolaboratory scale but not suitable for upscaling the process.

Another drawback of this method is that isolation and purification ofthe product is difficult since no solvent is used in the synthesis.

Still another drawback of this method is that purity of the CS obtainedis mainly dependent on the efficiency of the grinding.

Yet another drawback of this method is that it is a heterogeneousreaction and difficult to find the completion of the reaction if thegrinding efficiency is poor.

Other drawback of this method is that it requires special equipment,thus this process is not cost-effective also.

There is a need to develop an improved eco-frlendly and cost effectivemethod for the preparation of 2-chlorobenzylidenemalononitrile (CS) thatcan easily be up scaled to manufacturing process.

OBJECTS OF THE PRESENT INVENTION

The main object of the present invention is to provide an improvedprocess for the presentation of 2-chlorobenzylidenemalononitrile (CS).

Another object of the present invention is to provide an improvedprocess for the preparation of CS, which gives CS of high purity.

Yet another object of the present invention is to provide an improvedprocess for the preparation of CS wherein the water used as solved isrecycled to reduce the effluent load.

Still another object of the present invention is to provide an improvedprocess for the preparation of CS where in water is used as solvent.

Further object of the present invention is to provide an improvedprocess for the preparation of CS wherein the effluent can be disposedoff easily without any environmental pollution.

Yet further object of the present invention is to provide an improvedprocess for the preparation of CS which is cost effective.

Still further object of the present invention is to provide animprovement method for the preparation of CS which does not require anyspecial equipment.

The yield and purity of CS obtained is >99.5% and the melting point is92-940 (Reported mp 94° C.). The process is simple, does not pollute theenvironment and is eco-friendly.

DESCRIPTION OF INVENTION

According to this invention there is provided an improved process forthe preparation of 2-chlorobenzylidenemalononitrile (CS) comprising ofthe steps of:

-   (a) preparing malononitrile suspension by adding 5-20% (wt %)    preferably 12-14% malononitrile to water while constantly stirring    and then adding 0.05-0.5% (v/v) preferably 0.1-03% of a catalyst    like piperidine, pyridine, 2-picoline, 3-picoline, 4-picoline or    morpholine preferably piperidine with constant stirring at 20-30°    C.;-   (b) condensing the malononitrile suspension prepared in step (a)    with 2-chlorobenzaldehyde by adding 10-15% (v/v) preferably 25-30%,    of 2-chlorobenzaldehyde cover a period at 30-45 minutes so that the    temperature of the reaction mixture remains below 50° C., constantly    stirring for 20-40 minutes, then filtering the CS and drying it at    20-30° C. under water vacuum for 3-5 hrs.

The process of the present invention for the preparation of2-chlorobenzylidene malononitrile (CS) comprises of following steps:

Step (i): Preparation of Malononitrile Suspension:

In a bottom flask equipment with water condenser, mechanical stirrer andpressure-equalizing funnel, 5-20% (wt %) of malononitrile preferably12-14% (wt %) is added in water with stirring. To this, 0.05-05% v/vpreferably 0.1-0.3% v/v of catalyst like piperidine, pyridine,2-picoline, 3-picoline, 4-picoline or morpholine preferably piperidineis added with continuous stirring at 20-30° C.

Step (ii) Condensation with 2-chloroberzaldehyde

To the malononitrile suspension prepared in step (i), 10-15% (w/v) of2-chlorobenzaldehyde preferably 25-30% (w/v) is added over a period of30-46 minutes so that the temperature of the reaction does not go beyond50° C., and the reaction mixture is stirred continuously for another20-40 minutes. The white crystalline solid CS is filtering and dried at20-30° C. under water vacuum for 3-5 hrs. The filtrate (mother liquor)is used for the preparation of CS in subsequent batches.

The generation of effluent is reduced by using the mother liquorrepeatedly for 5-50 batches, preferably 10-15 batches, Instead of usingfresh water for each batch, for safe disposal of the mother liquorobtained after 5-50 cycles, it is taken in a three-necked round bottomflask equipment with water condenser abd mechanical stirrer. To thisflask sodium hydroxide (equivalent to 1 to 25% w/v, preferably 5-10% w/vof effluent) is added slowly and the mixture is refluxed for 2-6 hrs.After cooling the mixture to 20-30° C., the effluent is safely disposedoff in the municipal drainage system.

In every batch, the yield and purity of CS obtained is >99.5% and themelting point is 92.94° C. (Reported mp 94° C.).

This invention will now be illustrated with a working example, which isintended to be typical example to explain the technique of the presentinvention and is not intended to be taken restrictively to imply anylimitation to the scope of the present invention.

WORKING EXAMPLES Example 1

Water (5000 ml) was taken in a three-necked round bottom flask equippedwith thermometer, pressure equalizing funnel and magnetic stirrer. Tothis malononitrile (660.6 g, 10 moles) was added and then piperidine (10ml, 0.1 mole) was added with constant stirring. To this2-chlorobenzaldehyde (2108 g, 15 moles) was added slowly with continuousstirring through pressure equalizing funnel. The temperature of thereaction mixture was maintained at 50° C. during addition of2-chlorobenzaldehyde. The white crystalline solid CS thus obtained wasfiltered and then dried under vacuum (25 mm).

Mother liquor obtained after filtration of white solid was recycled forthe preparation of CS by the same procedure as mentioned above for tentimes. The mother liquor obtained after 10 cycles was taken inthree-necked round bottom flask, to this sodium hydroxide 250 g wasadded and the mixture was refluxed for 4 hrs. After cooling the mixtureto 25° C. and after analysis, the effluent was disposed off in themunicipal drainage system. The yield and purity of CS was >99.5% and themelting point is 92-94° C. (Reported mp 94° C.).

Example II

Water (5000 ml) was taken in a three neck round bottom flask equippedwith thermometer, pressure equalizing funnel and magnetic stirrer. Tothis malononitrile (660.6 g, 10 moles) was added and then piperidine (10ml, 0.1 mole) was added with constant stirring. To this2-chloroberzaldehyde (1405 g, 10 moles) was added slowly with continuousstirring through pressure equalising funnel. The temperature of thereaction mixture was maintained at 50° C. during addition of2-chloroberzaldehyde. The while crystalline solid CS thus obtained wasfiltered and then dried under vacuum (25 mm).

Mother liquor obtained after filtration of white solid was recycled forthe preparation of CS by the same procedure as mentioned above. Themother liquor obtained after 10 cycles was taken in three-necked roundbottom flask, to this sodium hydroxide 250 g was added and the mixturewas refluxed for 4 hrs. After cooling the mixture to 25° C. and afteranalysis, the effluent was disposed off in the municipal drainagesystem. The yield and purity of CS was >99.5% and the melting point was92-94° C. (Reported mp 94° C.).

Example III

Water (5000 ml) was taken in a three-necked round bottom flask equippedwith thermometer, pressure equalizing funnel and magnetic stirrer. Tothis malonontrile (991 g, 15-moles) was added and then piperidine (10ml, 0.1 mole) was added with constant stirring. To this2-chlorobenzaldehyde (1405 g, 10 moles) was added slowly with continuousstirring through pressure equalizing funnel. The temperature of thereaction mixture was maintained at 50° during addition of2-chlorobenzaldehyde. The white crystalline solid CS thus obtained wasfiltered and then dried under vacuum (25 mm).

Mother liquor obtained after filtration of white solid was recycled forthe preparation of CS by the same procedure as mentioned above. Themother liquor obtained after 10 cycles was taken in three-necked roundbottom flask, to this sodium hydroxide 250 g was added and the mixturewas refluxed for 4 hrs. After cooling the mixture to 25° C. and afteranalysis, the effluent was disposed off in the municipal drainagesystem. The yield and purity of CS was >99.5% and the melting point was92-94° C. (Reported mp 94° C.).

It is to be understood that the process of the present invention issusceptible to modification, changes, adaptations by those skilled inthe art, such modifications, changes, adaptation are intended to bewithin the scope of the present invention which is further set forthunder the following claims:

1-5. (canceled)
 6. An improved process for the preparation of2-chlorobenzylidenemalononitrile (CS), comprising the steps of: (a)preparing malononitrile suspension by adding 5-20% (wt %) malononitrileto water while constantly stirring and then adding 0.05-0.5% (v/v) of acatalyst selected from the group consisting of piperidine, pyridine,2-picoline, 3-picoline, 4-picoline and morpholine with constant stirringat 20-30° C.; (b) condensing the malononitrile suspension prepared instep (a) with 2-chlorobenzaldehyde by adding 10-15% (w/v) of2-chlorobenzaldehyde, cover for a period at 30-45 minutes so that thetemperature of the reaction mixture remains below 50° C., constantlystirring for 20-40 minutes, then filtering the CS and drying it at20-30° C. under water vacuum for 3-5 hours.
 7. The improved process forthe preparation of CS as claimed in claim 6, wherein the 12-14%malononitrile is added to the water, wherein 0.1-0.3% (v/v) of thecatalyst is added, wherein the catalyst is piperidine, and wherein themalononitrile suspension is condensed by adding 25-30% (w/v)chlorobenzaldehyde.
 8. The improved process for the preparation of CS asclaimed in claim 6, wherein the generation of effluent is reduced byrecycling the filtrate (mother liquor) obtained in step (b) for 5-50batches of preparation of CS.
 9. The improved process for thepreparation of CS as claimed in claim 8, wherein 10-15 batches of CS areprepared.
 10. The improved process for the preparation of CS as claimedin claim 8, wherein the mother liquor obtained after recycling for 5-50batches is treated with sodium hydroxide equivalent to 1-25% (w/v),refluxing for 2-6 hours, then cooling to 20-30° C. before disposing. 11.The improved process for the preparation of CS as claimed in claim 10,wherein treatment of the mother liquor with sodium hydroxide isequivalent to 5-10% (w/v) of effluent.
 12. The improved process for thepreparation of CS as claimed in claim 6, wherein the solvent used forthe process is water.